.TH std::destroy_n 3 "2024.06.10" "http://cppreference.com" "C++ Standard Libary"
.SH NAME
std::destroy_n \- std::destroy_n

.SH Synopsis
   Defined in header <memory>
   template< class ForwardIt, class Size >                                \fI(since C++17)\fP
   ForwardIt destroy_n( ForwardIt first, Size n );                        \fI(until C++20)\fP
   template< class ForwardIt, class Size >                                \fI(since C++20)\fP
   constexpr ForwardIt destroy_n( ForwardIt first, Size n );      \fB(1)\fP
   template< class ExecutionPolicy, class ForwardIt, class Size >
   ForwardIt destroy_n( ExecutionPolicy&& policy, ForwardIt           \fB(2)\fP \fI(since C++17)\fP
   first, Size n );

   1) Destroys the n objects in the range starting at first, as if by

 for (; n > 0; (void) ++first, --n)
     std::destroy_at(std::addressof(*first));

   2) Same as \fB(1)\fP, but executed according to policy. This overload participates in
   overload resolution only if

   std::is_execution_policy_v<std::decay_t<ExecutionPolicy>> is true.        (until
                                                                             C++20)
   std::is_execution_policy_v<std::remove_cvref_t<ExecutionPolicy>> is true. (since
                                                                             C++20)

.SH Parameters

   first             -          the beginning of the range of elements to destroy
   n                 -          the number of elements to destroy
   policy            -          the execution policy to use. See execution policy for
                                details.
.SH Type requirements
   -
   ForwardIt must meet the requirements of LegacyForwardIterator.
   -
   No increment, assignment, comparison, or indirection through valid instances of
   ForwardIt may throw exceptions.

.SH Return value

   The end of the range of objects that has been destroyed (i.e., std::next(first, n)).

.SH Complexity

   Linear in n.

.SH Exceptions

   The overload with a template parameter named ExecutionPolicy reports errors as
   follows:

     * If execution of a function invoked as part of the algorithm throws an exception
       and ExecutionPolicy is one of the standard policies, std::terminate is called.
       For any other ExecutionPolicy, the behavior is implementation-defined.
     * If the algorithm fails to allocate memory, std::bad_alloc is thrown.

.SH Possible implementation

   template<class ForwardIt, class Size>
   constexpr // since C++20
   ForwardIt destroy_n(ForwardIt first, Size n)
   {
       for (; n > 0; (void) ++first, --n)
           std::destroy_at(std::addressof(*first));
       return first;
   }

.SH Example

   The following example demonstrates how to use destroy_n to destroy a contiguous
   sequence of elements.


// Run this code

 #include <iostream>
 #include <memory>
 #include <new>

 struct Tracer
 {
     int value;
     ~Tracer() { std::cout << value << " destructed\\n"; }
 };

 int main()
 {
     alignas(Tracer) unsigned char buffer[sizeof(Tracer) * 8];

     for (int i = 0; i < 8; ++i)
         new(buffer + sizeof(Tracer) * i) Tracer{i}; //manually construct objects

     auto ptr = std::launder(reinterpret_cast<Tracer*>(buffer));

     std::destroy_n(ptr, 8);
 }

.SH Output:

 0 destructed
 1 destructed
 2 destructed
 3 destructed
 4 destructed
 5 destructed
 6 destructed
 7 destructed

.SH See also

   destroy           destroys a range of objects
   \fI(C++17)\fP           \fI(function template)\fP
   destroy_at        destroys an object at a given address
   \fI(C++17)\fP           \fI(function template)\fP
   ranges::destroy_n destroys a number of objects in a range
   (C++20)           (niebloid)
